The present invention relates to a new and improved construction of a device for detecting knot-like thick places in travelling textile threads or the like. It is known to use capacitive or optoelectrical transducers for detecting thick places in textile threads travelling at textile machines or through a testing device, and to process the electrical signals generated by the transducers in an electronic circuitry which produces output signals indicative of the presence of such thick places.
Moreover, from German patent No. 1,101,018 there is known a mechanoelectrical device for detecting thick places and knots in threads or rovings and twisted yarns, where the thread material to be tested travels through a slot of a guage which is set to the nominal thickness value of the thread material, and where an electrical contact system is actuated, by means of resilient feeler members, when said nominal thickness value is exceeded, causing the thread travel to be stopped and/or a counting device to be tripped.
Capacitive or optoelectrical transducers or sensing devices which operate without touching the thread work accurately and without inertia even at high yarn speeds, however, they are expensive to manufacture. On the other hand, mechanoelectrical sensing devices exhibit a certain amount of sluggishness or inertia owing to the relatively great mass of the feeler member touching the thread. Thus, such mechanoelectrical sensing devices do not work in a satisfactory manner at high yarn travel speeds.